1. Field of the Invention
The present invention relates to prostheses, including, without limitation, knee prostheses. In particular, some implementations of the present invention relate to systems and methods for providing prosthetic implants that are relatively lightweight. While the implants can be produced in any suitable manner and have any suitable feature that allows them to be lightweight, in some instances, such implants include an internal lattice structure that supports the implants, while allowing the implants to be relatively lightweight and rigid.
2. Background and Related Art
Orthopedic surgeons are experiencing a proliferation of joint replacement surgeries. This demand appears to be driven by the fact that few procedures return as much quality of life as do joint replacements.
One common joint replacement surgery that can be especially useful in returning quality of life to an individual is that of knee replacement surgery. In this regard, the increased need for knee replacements implicates the need for durable and long lasting artificial knee devices that provide for and allow full, functional flexion. That is, there is a great need for research that provides new medical advances on the overall function and performance of knee prostheses, and improves corresponding surgical materials and technologies related to such devices.
Improvements to knee prostheses correspondingly increase with demand. Thus, currently-available knee prostheses mimic characteristics of the normal knee more than those previously used. Unfortunately, some of today's knee prostheses still have shortcomings.
Among these shortcomings is the inability of a knee prosthesis patient to achieve deep knee flexion, also known as full functional flexion. Though some currently available knee prostheses allow for knee flexion (i.e., bending) of more than 130° from full limb extension (0° being when the patient's knee is fully extended and straight); some such prostheses do not allow patients to flex from full extension to 160° and beyond (e.g., to full functional and/or deep knee flexion). Full functional or deep knee flexion is where the leg is bent to its maximum extent, which may be with the femur and tibia at an angle to each other of 140° or more, though the actual angle varies from person to person and with body habitus.
To illustrate the average range of knee motion in degrees achieved by patients having standard knee prostheses surgery, the following is provided: When a patient's knee or limb is fully extended, the femur and tibia are typically in the same plane at 0°, or up to 5-10° of hyperextension in some individuals. However, once the knee bends, and the distal tibia moves toward the buttocks, the angle increases from 0° to 90° for a person sitting in a chair. Furthermore, when the tibia is closest to the femur, and the heel is almost at, if not touching, the buttock, the angle is around 160° or more. Most conventional knee prosthesis patients are unable to consistently achieve the latter position or any position placing the knee joint at angles above 130° (e.g., at 160° and beyond).
For many people, such a limb and body position is not often achieved or desired most of the time. However, nearly everyone, at some point in time, whether or not it occurs when a person is getting on and off the ground to play with children, or merely incidental to living an active lifestyle, finds themselves in a position requiring knee flexion greater than 130°. Unfortunately, those with currently-available knee prostheses are unable to participate in any activity requiring greater knee flexion and are thus limited to watching from the sidelines.
In many populations and cultures such a limb/knee and body position is desired and necessary the majority of the time. For instance, in some Asian and Indian cultures, full functional flexion and the squatting position is common and performed for relatively long periods of time.
A need, therefore, exists for knee prostheses for those patients and especially for those in cultures where extensive squatting, sitting with knees fully flexed, and/or kneeling when praying or eating is common, to achieve knee flexion greater than presently possible among some of those who have currently-available knee prostheses.
As another example of a potential shortcoming associated with some conventional knee prostheses, some such prostheses are relatively heavy. Nevertheless, in many cases such prostheses are implanted into elderly recipients or, even if the prostheses are implanted into younger recipients, the implants are intended to remain with their recipients until such recipients age and eventually die. Accordingly, there is a need for prosthetic implants that are relatively lightweight and that do not require their recipients to carry unnecessary weight from such implants throughout their life.
As still another potential shortcoming, some conventional prostheses are relatively more rigid then the bones into which they are implanted. For instance, in some cases, a prosthetic stem extending in a medullary canal is more rigid then the cancellous bone around such a stem. As a result, in some cases, bone surrounding the rigid stem may not flex as it should. In this regard, as such a bone may experience less of the flexion forces than would typically strengthen the bone, such a bone may actually become weak and resorb. Additionally, in some cases as the bone surrounding a rigid shaft flexes, micro-abrasions may occur at the interface between the bone and the stem, resulting in the loss of bone at the interface. Moreover, in some instances in which a prosthetic implant keeps a portion of a long bone rigid, stresses that would normally be spread across a length of the bone are spread across a smaller area of the bone, often forming a stress riser in the bone at an end of the prosthetic (e.g., at an end of a rigid stem).
As still another example, some femoral prostheses place relatively large loads on the distal end of the femur, and do little to dissipate such loads. As a result, some such prostheses may do little to prevent fractures from forming and spreading in the femur (e.g., at stress risers created as a consequence of bone cuts that were made to allow the femoral prosthesis to be seated on the femur).
As yet another example, although some femoral prostheses comprise a stem to strengthen the femur's distal end, such stems often place significant limits on the physical characteristics of the femoral prosthesis that can be used therewith. Additionally, in some cases in which a femoral prosthesis includes a stem, the stem can also limit the manner in which the femoral prosthesis can be attached to a femur.
Thus, while techniques currently exist that relate to prosthetic implants (such as knee prostheses), challenges with such implants still exist, including those discussed above. Accordingly, it would be an improvement in the art to augment or even replace current techniques with other techniques.